Nitrogen Recovery in Tropical Agroecosystems: Insights from a US Study

Strategic Insights -

A team of researchers from the University of California has conducted a comprehensive study on nitrogen recovery in tropical agroecosystems. The researchers analyzed data from 13 diverse tropical agroecosystems and revealed that limited nitrogen availability is a major obstacle to increasing crop yields. The study aimed to determine the total recovery of nitrogen-15 (N-15) from inorganic and organic sources, with results indicating that soil nitrogen remains the primary source of nitrogen for crops.

Key Takeaways:

  • The researchers found that between 7 and 58% (average of 21%) of crop nitrogen uptake during the first growing season was derived from fertilizer.
  • On average, 79% of crop nitrogen was derived from the soil, indicating that soil nitrogen is the primary source of nitrogen for crops.
  • The study revealed that N-15-labeled residues were applied, and in the first growing season, 4% of crop nitrogen was derived from the residues.
  • Average recoveries of N-15-labeled fertilizer and residue in crops after the first growing season were 33 and 7%, respectively.
  • Corresponding recoveries in the soil were 38 and 71%, indicating that more than 90% of residue nitrogen was retained in the soil.
  • An additional 6% of fertilizer and 9.1% of residue was recovered by crops during subsequent growing seasons, with a total N-15 recovery average of 54% between N from fertilizer and N from residue.
  • After five growing seasons, more residue nitrogen (40%) than fertilizer nitrogen (18%) was recovered in the soil, better sustaining the soil organic matter nitrogen content.
  • Long-term total recoveries of N-15-labeled fertilizer or residue in the crop and soil were similar.
  • The researchers concluded that management practices to improve N use efficiency and reduce losses in wet tropical regions will remain a challenge.

Statistics:

  • Between 7 and 58% (average of 21%) of crop nitrogen uptake during the first growing season was derived from fertilizer.
  • On average, 79% of crop nitrogen was derived from the soil.
  • Average recoveries of N-15-labeled fertilizer and residue in crops after the first growing season were 33 and 7%, respectively.
  • Corresponding recoveries in the soil were 38 and 71%.
  • An additional 6% of fertilizer and 9.1% of residue was recovered by crops during subsequent growing seasons.
  • After five growing seasons, more residue nitrogen (40%) than fertilizer nitrogen (18%) was recovered in the soil.

Sources:

  • Douradoneto, D. et al. (2010). Multiseason Recoveries of Organic and Inorganic Nitrogen-15 in Tropical Cropping Systems. Soil Science Society of America Journal, 74(1), 139-152.
  • University of California, Dept. of Plant Science, Davis, CA 95616, USA
  • Soil Science Society American, 677 South Segoe Road, Madison, WI 53711, USA.